as biodiesel says..

make sure the engine is really hot, when I did mine I removed the engine fan and intake manifold and started unscrewing them with engine running, only a couple of threads and then shut it off from the IP vacuum pod.

repeated on every plug - still had to use some creative methods including split a split nut tool and a few other pieces as stacks to pull it out.

about 4 or 5 months ago i was browsing and found a video on videomotion of a guy removing GPs on an OM604 engine, he was also doing it hot but he also made a slide hammer to pull them outwards.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

If you leave a dead plug in the engine, I suspect that would promote carbon build-up on the plug. Supposedly the reason why some plugs break off is because of carbon build-up. You may be risking a broken plug or two...

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

I nursed my E300 through the winter when the plugs started to go, but I wouldn't do it again. I found that when one goes, the others are not far behind.

When the last one went bad I would shoot a little ether in the intake and it worked startlingly well. Just don't use it with live plugs, I heard it does very bad things!

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I usually change all of them at once when one or two go bad.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

yes that is very plausible, I read a very similar comment in an old nissan diesel engine repair manual which also has 5 inch long glow plugs. It was translated poorly into english but it said that operating the engine with a bad glow plug combined with short distances can sieze the glow plug in the cylinder head.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Finally got around to installing the block heater cord. So should be all set regardless.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I've been doing that for many years. Never burned out a glow plug after doing that.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked